1. Field of the Invention
The present invention relates to a management apparatus that manages an exposure apparatus, an exposure method that uses the management apparatus, and a method of manufacturing a device using the exposure method.
2. Description of the Related Art
In recent years, semiconductor technologies are progressing at an increasing pace. To keep up with this trend, micropatterning techniques are also making remarkable progress. Especially photofabrication techniques using exposure apparatuses, which play a central role in the manufacture of semiconductors, have achieved the formation of patterns with feature sizes as small as 100 nm or less. To enhance the productivities of such exposure apparatuses, the types and timings of lots to be fed to them are controlled online in semiconductor device factories. On a semiconductor production line including a plurality of production processing steps, product groups as processing objects, and lots as semifinished product groups are transferred to each step in accordance with a predetermined step order, and undergo predetermined production processing in each step. On the above-mentioned production line, a wide variety of lots are processed in parallel. In each step mentioned above, the lots which have arrived at the step are classified based on their degrees of urgency (the degrees of urgency of production processing completion), and lots with high degrees of urgency are assigned higher priority levels in the order of arrival at the step, and are processed in accordance with the priority levels. Alternatively, in each step, the operator determines the processing order of lots according to circumstances involved, and their processing takes place. However, when the processing order of lots is determined using only two types of information: the degrees of urgency and the order of arrival in each step, as described earlier, this is insufficient to reflect the actual conditions of each step, which change with time, such as the number of workpieces in each step, and the degree of progress of production processing of each lot. Therefore, it is often the case that lots including relatively large numbers of workpieces are processed ahead of those including relatively small numbers of workpieces, and are transferred to the next step, resulting in nonuniformity in load imposed on each step. This degrades the production efficiency over the entire production line.
To combat this situation, Japanese Patent Laid-Open No. 4-13548 discloses a method of assigning priority levels to processing objects by the following procedure, and a management apparatus which performs this method. First, a plurality of evaluation items for determining the index of the order of priority are determined in advance based on the status of production processing, and the status of production processing, which is necessary to evaluate these items, is detected. Next, the evaluation index of each evaluation item is obtained for each processing object based on the detection result. The evaluation indices are weighted to adjust the degrees of influence that the evaluation items exert on the order of priority, the weighted evaluation indices are summed up for each processing object, and higher priority levels are assigned in turn from a processing object with a largest summed evaluation index.
To fabricate a semiconductor device, an exposure apparatus transfers an electronic circuit pattern onto a silicon wafer (to be simply referred to as a wafer hereinafter) which serves as a foundation for fabricating the semiconductor device. This exposure apparatus includes a projection optical system with its aberration known to change depending on exposure energy, which is supplied to the projection optical system and determined based on the exposure conditions under which the wafer is processed. The exposure conditions which exert an influence on the aberration of the projection optical system are, for example, the illumination mode, a diffracted light distribution generated by the pattern of a reticle, the exposure processing time, the reticle transmittance, the shot area, the number of shots, the reflectance of the wafer surface, the resist type and film thickness, the resist process, and the exposure dose. The technique described in Japanese Patent Laid-Open No. 4-13548 sets the order of priority in accordance with the status of production processing, but does not take account of a change in aberration of a projection optical system of an exposure apparatus. To overcome this situation, with a technique which has recently been developed, an aberration correction system is mounted in a projection optical system to cancel a change in aberration upon partially absorbing exposure energy by the projection optical system, thereby suppressing the change in aberration upon absorbing exposure energy by the projection optical system.
Unfortunately, high-order aberrations to be corrected often remain in the aberration correction system, depending on the exposure energy distribution in the projection optical system. In this case, to expose the wafer free from any positional shift, lot charging into the exposure apparatus needs to be suspended until the aberration of the projection optical system falls below an allowable value. Therefore, the conventional technique poses a problem that the number of wafers processed per day is relatively small, and this degrades the productivity. Also, to suppress the change in aberration upon absorbing exposure energy by the projection optical system, another method slows down the processing speed so as to prevent the exposure energy from exceeding a preset limit. However, this method poses a problem that the number of wafers processed per day is relatively small as well.